Can you post a screenshot of the General Settings for that page? We’ll need to see the Folder and Filename settings.
My guess is you have a page (“books”) that is a sub-page of “library” (whose folder is set to “library”), and that you have “library/books” as the folder name for the “Books” page. If that’s the case, then just omit “library” from the folder name. Unless you put in an absolute path, RapidWeaver puts sub-pages in sub-folders of it’s parent page.
You want the “library” page to be:
You want the "books page to be: